Joints (pipe joints) used with fluid pipes that pass fluids through the interior are often capable of being detached to allow for easy replacement and repairs when the pipe deteriorates or when the fluid supply source deteriorates. Pipe joints have various threaded structures according to their application.
In air conditioners or the like, a refrigerant flows through a fluid pipe, and flare joints are often used as pipe joints. Recently, in view of their effects on global warming, studies or practical steps have been made to replace chlorofluorocarbon (CFC) refrigerants with carbon dioxide or alternative CFCs having a high design pressure, or with flammable hydrocarbon-based materials.
For example, when a hydrocarbon is used as the refrigerant, the pressure at which the hydrocarbon is used is about 3 MPa and the joint should withstand the same pressure as a conventionally used CFC refrigerant, but since the hydrocarbon is flammable, the requirement to prevent the refrigerant from leaking through the joint must be even more stringent than before.
Also, when carbon dioxide or an alternative CFC having a higher design pressure than that of a conventional CFC is used as the refrigerant, a pipe joint requires a higher pressure resistance than before.
Therefore, a flareless joint suitable for use at higher pressures than a flared joint must be used.
FIG. 6 shows an example of a conventional general-purpose flareless joint. FIG. 6A shows the joint before a nut 102 has been tightened, and FIG. 6B shows the joint after the nut 102 has been tightened. As shown in FIG. 6, the joint is configured from a joint main body 101, a nut 102, and a sleeve 103 provided between the two, and the structure is designed so that the distal end of the sleeve 103 is wedged onto a pipe 111 to connect the pipe 111 to the joint main body 101. Such a flareless joint has conventionally been used in thick steel pipes, but recently has come to be used to connect thin stainless steel pipes as well.
Japanese Examined Utility Model Application No. 61-26705 discloses a flareless joint used to connect thin stainless steel pipes for indoor piping. A structure is disclosed therein in which a sleeve made of a steel pipe is bent by tightening to prevent the pipe from collapsing when the distal end of the sleeve is wedged onto the pipe.
Japanese Patent Application Laid-Open No. 2001-159481 depicts a flareless joint used to connect thin gas pipes used in coolant piping for machine tools. When an O-ring and one end of a collet are inserted in the stepped portion of the joint main body, a space is formed between the end face of the joint main body and the end face of a projection provided on the outside-diameter portion of the collet. When the collet is tightened with a nut to bring the two end faces in contact with each other, a specific sealing pressure is achieved by the O-ring, and when the nut is tightened further to a specific position, a pawl provided to the inside-diameter portion of the collet is wedged onto the pipe to achieve a specific connecting force.